Transcranial Direct Current Stimulation (tDCS) with weak currents is a non-invasive, low-cost, and well tolerated technique producing lasting functional changes in the central nervous system. There is increasing evidence supporting the use of tDCS to improve stroke rehabilitation. Behavioral and therapeutic outcomes of tDCS depend on the brain areas being targeted. However, conventional approaches are limited in that they insufficiently activate the target region and/or result in nonspecific stimulation throughout the entire head. To address this, High- Definition tDCS (HD-tDCS), which uses arrays of specifically designed electrodes, has been developed and is being tested for a number of indications, including stroke rehabilitation and central pain. The high-definition approach allows for exceptional flexibility in designing targeted and individualized electrotherapy. Preliminary work in a Phase I STTR demonstrated that the HD approach, when individualized using MRI and fMRI to account for the specific stroke anatomy, can achieve increased stimulation on active peri-lesional areas, which are hypothesized to mediate the gains of language rehabilitation treatment. A preliminary trial indicated that this may result in improved outcomes for the treatment of aphasia. Additionally, hardware and software development in Phase I STTR make a larger clinical trial now feasible. The present proposal is a direct continuation of the STTR work using the alternate SBIR mechanism. The first specific aim in Phase I is to adapt our existing HD-tDCS hardware technology to develop a HD device that allows true double-blinding. The second aim of Phase I is to establish the patient-specific modeling and targeting pipeline developed at City College of New York at Soterix Medical in order to execute a trial on a larger cohort of subjects. The first specific aim in Phase II is to perform a carefully controlled double-blind randomized prospective trial for the adjunctive treatment of aphasia with HD-tDCS. The primary outcome measure is an improvement in the ability to name common objects, which is a major impairment for persons with aphasia. The expected efficacy in naming corresponds to clinically meaningful improvements in language overall. The second aim of Phase II is to optimize treatment parameters to further increase this effect size and to elucidate the mechanism of action by assessing brain function with fMRI before and after treatment. The trial adopts an established treatment protocol and patient selection criteria so as to compare the results with conventional tCDS using unoptimized sponge-based electrodes. In addition, device technology and regulatory process will be developed to be ready for a pivotal FDA-regulated Phase III clinical trial. The long-term goal of this project is to increase the efficacy of this ne and versatile treatment option for stroke rehabilitation, and to make it broadly accessible to patients and clinicians by making it commercially available.